Rack and pinion gear arrangements have been utilized for the transformation of motion from one direction to another direction. For example, rotary motion produced by a motor may be transformed through a gearing arrangement of a rack and pinion gear to linear motion. Such gears, however, when used for moving large objects, require a large power source, add additional weight to the drive system, require lubrication and further require extensive maintenance.
Chain drive systems have been utilized as an alternative drive system for a rack and pinion gear arrangement. In such systems, a chain may form a loop around the object to be moved. The chain may be driven through a drive gear by a motor or other power source to in turn move the object. However, such systems, when utilized to move large objects, require great lengths of chain having stressed and unstressed portions. Since the chain is typically unsupported around the objects, the chain may not completely engage the object to be moved and if the chain is stressed in various amounts over its length, stretch of the chain occurs. The undesirable nature of chain stretch is readily apparent in that repetitive accurate movement of the object cannot be consistently achieved since the length of the chain varies. Additionally, as the chain permanently stretches, slack is introduced into the system which must be taken up by the driven gears before the object can be moved. This slack results in a delayed movement of the object after the drive system is actuated.
A need has thus arisen for a chain drive system in which relatively short load sections of chain can be utilized for moving large objects and wherein chain stretch is minimized. Additionally, a need has arisen for a chain drive system in which stress is minimized to reduce the load on the chain links.